When a photoresist coating film is formed on a substrate having a concave portion such as a trench or a hole, it becomes difficult to form a suitable coating film as the concave portion becomes deeper. For example, when a coating liquid of low concentration is used, it is difficult to make the surface of the coating film flat. On the other hand, when a coating liquid of high concentration is used, there is a possibility that the coating film with a gap is formed in the concave portion. In these cases, there is a problem that a suitable resist pattern cannot be formed of the photoresist coating film.
Moreover, when this resist film is used as a mask to implant ions into the substrate at the bottom of the concave portion, it is necessary to remove the resist film in the concave portion to form the resist pattern. In this case, it is necessary to sufficiently develop the resist film in the vicinity of the bottom of the concave portion and remove it. However, when the concave portion is deep, there is a possibility that the resist film in the vicinity of the bottom of the concave portion is not sufficiently developed and the resist film is left at the bottom of the concave portion. Therefore, there is a problem even in this case that a suitable resist pattern cannot be formed.